A wave vector is a vector that encodes wavelength and direction of a plane wave.
Let and write the Cartesian space of dimension . Thinking of as a vector space, then each point in it is a vector and hence a smooth function may be thought of as a function of these “position vectors”.
If is a function with rapidly decreasing partial derivatives, then its Fourier transform exists. By the Fourier inversion theorem, this function is such that it expresses as a superposition of “plane wave” functions as
Here the vector determines
the wavelength (the inverse of the norm of );
the direction (the corresponding unit vector in the unit sphere)
of the “plane wave” .
The product is also called the wave number and then the wave number vector. Beware that elsewhere the wave number vector is denoted “”, which makes the “wave vector” become . (See e.g. Wikipedia, “Physics definition” as opposed to “Crystallography definition”.)
If here is identified with Minkowski spacetime with canonical coordinates denoted , then the 0-component of the wave vector
is called the frequency of the corresponding plane wave (in the chosen coordinate system); this is the angular frequency.
plane waves on Minkowski spacetime
See also
Last revised on August 2, 2018 at 07:11:17. See the history of this page for a list of all contributions to it.